1. Technical Field of the Invention
This invention is related to communication receivers, and more specifically to receivers utilizing burst processing.
2. Background of the Art
As the demand for telecommunication bandwidth has grown dramatically in recent years, it has become increasingly problematic to provide cost-effective, continuous connections in many applications that require high, instantaneous throughput due to the inherent presence of bursty information transmissions. Thus, the implementation of multiple-access systems has realized significant growth. These multiple-access systems share channel bandwidth by providing access to users only when they need it.
Burst processing is utilized in a variety of digital cellular communications such as GSM (Global System of Mobile Communications), IS-136 cellular phones and packet data networks. In the data packet regime, accommodating such a technology requires the introduction of a specialized kind of modem called a burst modem that can receive and transmit modulated data packets in short bursts.
An MF-TDMA (Multiple Frequency-Time Domain Multiple Access) architecture is a frequency-hopping access technique where users may transmit on any carrier. An incoming packet is fragmented into cells and transmitted in the user-assigned TDMA slots, or in designated random-access slots. Dependent on how the return link bandwidth is allocated, these TDMA slots could be on different carriers requiring a Very Small Aperture Terminal to “hop” between carriers on a slot-by-slot basis.
In the return link MF-TDMA structure of a satellite transmission system, multiple users each require, essentially, a continuous connection on a common channel, however, the connection is provided by assigning each user a periodic time slot in which to insert data on a channel whose bandwidth is substantially greater than that required by any single user. Each user can then send bursts of data at a specified frequency and during a specific time slot.
In continuous modem applications, the user typically waits a few seconds while the receiver acquires the transmitted signal. However, in a burst modem, where the user times contribute to an unacceptable amount of overhead to the system, and substantially reduce the system capacity. From the modem designer's perspective, it is the channel that substantially alters the received signal from the transmitted signal. Therefore, the burst modem requires an acquisition architecture that quickly filters out channel noise in the incoming signal by rapidly estimating the appropriate receiver gain, the carrier phase and frequency, the sample timing frequency, and phase. For example, in a star return link, transmission bursts of 512 QPSK (Quadrature Phase Shift Keying) symbols are sent. The actual carrier frequency of each burst can vary by as much as 10% of the symbol rate, and the burst arrival time can be early or late by up to eight symbol times.
What is needed is a burst-reception architecture capable of processing records of burst information in the presence of significant channel noise.